Buffered negative electrode-electrolyte assembly, battery, and method of manufacture thereof

ABSTRACT

A buffered negative electrode-electrolyte assembly includes: a porous negative electrode comprising a metal, a transition metal nitride, or a combination thereof; a solid-state electrolyte; and a buffer layer between the porous negative electrode and the solid-state electrolyte. The buffer layer comprising a buffer composition according to Formula (1) M m N n Z z H h X x . The buffer composition has an electronic conductivity that is less than or equal to 1×10 −2  times an electronic conductivity of the solid-state electrolyte, and the buffer composition has an ionic conductivity less than or equal to 1×10 −6  times an ionic conductivity of the solid-state electrolyte.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 63/065,353, filed on Aug. 13, 2020, in the United States Patent andTrademark Office, and all the benefits accruing therefrom under 35U.S.C. § 119, the content of which is incorporated herein in itsentirety by reference.

BACKGROUND 1. Field

Disclosed is a buffered negative electrode-electrolyte assembly, abattery including the same, and a method of manufacture thereof.

2. Description of the Related Art

A solid-state lithium battery can potentially offer improved safety, andin some configurations provide improved specific energy and energydensity. However improved reliability is desired. It is understood thatdetachment of the solid electrolyte from the negative electrodecontributes to battery failure. Thus, there remains a need for improvedmaterials to improve the performance of solid-state lithium batteries.

SUMMARY

A buffered negative electrode-electrolyte assembly comprises:

a porous negative electrode comprising a metal, a transition metalnitride, or a combination thereof;

a solid-state electrolyte; and

a buffer layer between the porous negative electrode and the solid-stateelectrolyte, the buffer layer comprising a buffer composition accordingto Formula (1)

M_(n)N_(n)Z_(z)H_(h)X_(x)   (1)

wherein

M is Na, K, Rb, Cs, Al, or a metal of Group 2 or 3, or a combinationthereof, wherein

m is 1, 2, 3, or 4,

X is at least one halogen and wherein x is 0, 1, 2, or 6,

Z is O, S, or a combination thereof, and z is 0, 1, 2, 3, or 4,

n is 0, 1, or 2, and

h is 0, 1, 2, or 3,

provided that x+z+n+h is at least 1,

wherein

the buffer composition has an electronic conductivity that is less thanor equal to 1×10⁻² times an electronic conductivity of the solid-stateelectrolyte, and the buffer composition has an ionic conductivity lessthan or equal to 1×10⁻⁶ times an ionic conductivity of the solid-stateelectrolyte.

In another aspect, an electrochemical cell comprises: a positiveelectrode; and the buffered negative electrode-electrolyte assembly asdescribed above on the positive electrode.

The electrochemical cell is manufactured by disposing a buffer layerbetween a solid-state electrolyte and a porous negative electrode toform the above described buffered negative electrode-electrolyteassembly; and disposing a positive electrode on the solid-stateelectrolyte to manufacture the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages and features of this disclosure willbecome more apparent by describing in further detail exemplaryembodiments thereof with reference to the accompanying drawings, inwhich:

FIG. 1 is a schematic diagram of an embodiment of an electrochemicalcell including a buffered negative electrode-electrolyte assembly;

FIG. 2 is a schematic diagram illustrating the mechanism of a potentialfailure of a battery having an ionic conductive isolator;

FIG. 3 is a schematic diagram illustrating the mechanism of a potentialfailure of a battery having an electronic conductive isolator;

FIG. 4 is a schematic diagram illustrating the mechanism of a potentialfailure of a battery having a chemically active isolator;

FIG. 5 is a schematic diagram of an embodiment of an electrochemicalcell including a buffer layer disposed on the roots of thenanostructures in a negative electrode;

FIG. 6 is a schematic diagram of an embodiment of an electrochemicalcell including a buffer layer forming a conformal coating on a negativeelectrode;

FIG. 7A and FIG. 7B are scanning electron microscopy (SEM) images oferbium (III) oxide coated titanium nitride electrode of Example 1;

FIG. 8A is a graph of voltage (volts) versus time (hours) illustratingthe results of charging and discharging an electrochemical cell having abuffered negative electrode-electrolyte assembly;

FIG. 8B is a graph of current (milliamperes) versus time (hours) showingthe current when obtaining the results shown in FIG. 8A; and

FIG. 9 is a schematic diagram of an embodiment of a lithium battery.

DETAILED DESCRIPTION

A solid-state lithium battery includes a negative electrode, a positiveelectrode, and a solid-state electrolyte between the negative electrodeand the positive electrode. It is understood that the positive electrodecould alternatively be referred to as a cathode, and the negativeelectrode as an anode. For the solid-state negative electrode, use oflithium metal or a lithium alloy negative electrode active material isdesired because lithium metal or lithium alloy negative electrode activematerials can potentially provide improved specific capacity and energydensity. However, maintaining contact between the solid-stateelectrolyte and such negative electrode active materials remains as apersistent problem. While not wanting to be bound by theory, it isunderstood that as the cell is charged and discharged, lithium ions tendto reduce and precipitate at the interface between the solid-stateelectrolyte and the negative electrode active material. The volume ofthe deposited lithium eventually leads to a loss of contact between thesolid-state electrolyte and the negative electrode active material. Suchreduction of contact can be detrimental for the battery operation, beingone of the main causes of battery failure. In extreme cases, suchreduction of contact can lead to partial or full detachment of thenegative electrode from the solid-state electrolyte, creatingeffectively an open circuit system.

Use of porous negative electrodes (e.g., nanostructured metal anodes)has been suggested to provide spaces to accommodate the depositedlithium within the nanostructure scaffold. Nonetheless, detachment canstill occur. While not wanting to be bound by theory, it is understoodthat during cycling metal ions tend to chemically reduce and thusprecipitate at the interface between the solid-state electrolyte and theporous negative electrode structure. It is understood that with furthercycling, precipitation of lithium can still lead to a loss of contactbetween the solid-state electrolyte and the surface of the porousnegative electrode structure, contributing to battery failure.

The inventors have discovered that adding a buffer layer as describedherein between a solid-state electrolyte and a porous negative electrodecan address and solve the problem of solid-state electrolyte detachmentfrom the negative electrode.

A buffered negative electrode-electrolyte assembly is disclosed. Asillustrated in FIG. 1, the buffered negative electrode-electrolyteassembly (15) comprises a porous negative electrode (18); a solid-stateelectrolyte (14); and a buffer layer (16) between the porous negativeelectrode (18) and the solid-state electrolyte (14).

In an aspect, the buffer layer is an electronic insulator relative tothe solid-state electrolyte. In an aspect, the buffer layer comprises abuffer composition having an electronic conductivity that is less thanor equal to 1×10⁻² times, less than or equal to 0.5×10⁻² times, lessthan or equal to 0.1×10⁻² times an electronic conductivity of thesolid-state electrolyte. In an aspect, the buffer composition has anelectronic conductivity that is greater than or equal to 1×10⁻⁸ times,greater than or equal to 1×10⁻⁷ times, or greater than or equal to1×10⁻⁶ times an electronic conductivity of the solid-state electrolyte.An electronic conductivity of the buffer composition can have be greaterthan or equal to 1×10⁻¹⁴ Siemens per meter (S/m), greater than or equalto 1×10⁻¹³ S/m, or greater than or equal to 1×10⁻¹² S/m, to 1×10⁻⁶ S/m,1×10⁻⁷ S/m, or 1×10⁻⁸ S/m. The electrical conductivity can be determinedaccording to ASTM B-193, “Standard Test Method for Resistivity ofElectrical Conductor Materials,” e.g., at 20° C., or according to ASTME-1004, “Standard Test Method for Determining Electrical ConductivityUsing the Electromagnetic (Eddy-Current) Method,” e.g., at 20° C.Additional details may be determined by one of skill in the art withoutundue experimentation. The electronic conductivity of the buffercomposition and the electronic conductivity of the solid-stateelectrolyte are measured under the same conditions.

If the buffer layer is not an electronic insulator relative to thesolid-state electrolyte, lithium deposition may occur at the interfacebetween the solid-state electrolyte and the buffer layer, resulting indetachment of the solid-state electrolyte from the surface of the bufferlayer. While not wanting to be bound by theory, it is understood that,as illustrated in FIG. 2, if the buffer layer (17) is electronicallyconductive relative to the solid-state electrolyte, electrons (e⁻) cantravel through the buffer layer (17) and encounter lithium ions (Li⁺) atthe interface of the solid-state electrolyte (14) and the buffer layer(17), forming lithium metal (19). As cycling continues, the depositedlithium metal (19) can have a volume sufficient to result in a loss ofcontact between the solid-state electrolyte (14) and the porous negativeelectrode (18), contributing to battery failure.

In an aspect, the buffer layer is also an ionic insulator relative tothe solid-state electrolyte. In an aspect, the buffer composition has anionic conductivity that is less than or equal to 1×10⁻⁶ times, less thanor equal to 0.5×10⁻⁶ times, less than or equal to 1×10⁻⁷ times, or lessthan or equal to 1×10⁻⁷ times an ionic conductivity of the solid-stateelectrolyte. In an aspect, the buffer composition has an ionicconductivity that is greater than or equal to 1×10⁻¹⁴ times, greaterthan or equal to 1×10⁻¹² times, greater than or equal to 1×10⁻¹⁰ times,or greater than or equal to 1×10⁻⁸ times an ionic conductivity of thesolid-state electrolyte. Ionic conductivity may be determined by acomplex impedance method at 20° C., further details of which can befound in J.-M. Winand et al., “Measurement of Ionic Conductivity inSolid Electrolytes,” Europhysics Letters, vol. 8, no. 5, p. 447-452,1989. The ionic conductivity of the buffer composition and the ionicconductivity of the solid-state electrolyte are measured under the sameconditions.

If the buffer layer is not an ionic insulator relative to thesolid-state electrolyte, the battery may fail after cycling. Asillustrated in FIG. 3, when the buffer layer (11) is ionicallyconductive relative to the solid-state electrolyte (14), lithium ions(Li⁺) from the positive electrode can travel through the solid-stateelectrolyte (14) and the buffer layer (11) and encounter electrons (e⁻)at the interface (25) of the buffer layer (11) and the negativeelectrode (18), forming lithium metal (29). As the cycling continues,the volume of the deposited lithium metal (29) at the interface of thebuffer layer (11) and the negative electrode (18) may be sufficient tolead to a loss of contact between the solid-state electrode (14) and theporous negative electrode (18), contributing to battery failure.

In an aspect, the buffer layer is further stable, e.g.,thermodynamically stable, when contacted with the negative electrode andthe solid-state electrolyte. In other words, the buffer composition hasminimal or no chemical reaction with the negative electrode activematerial or the solid-state electrolyte. If the buffer composition isnot thermodynamically stable, a passivation layer (35) may form betweenthe buffer layer (36) and the solid-state electrolyte (34) as shown inFIG. 4. In an aspect, the passivation layer may be undesirablyresistive.

In an aspect the buffer layer composition is stable in the presence ofor when contacted with lithium. In an aspect, the buffer composition hasminimal or no discernable chemical reaction with the negative electrodeactive material or the solid-state electrolyte. In an aspect, in a phasediagram of the buffer layer composition and lithium, the buffer layercomposition is directly connected to lithium with a tie-line, with nointervening compounds between lithium and the buffer layer composition.

The buffer layer can adhere to the solid-state electrolyte and theporous negative electrode. In an aspect, the buffer layer serves as abinder, between the solid-state electrode and the porous negativeelectrode. Preferably, the interface between the porous negativeelectrode and the buffer layer, and the interface between the bufferlayer and the solid-state electrolyte both have an adhesion strengthsuch that it is possible to transmit at least 10 MPa to 1 GPa tensileand shear stresses across these interfaces without detachment of theporous negative electrode from the solid-state electrode. In an aspectthe adhesive force between the buffer layer and the solid-stateelectrolyte is greater than 0.5 N/m. Such adhesive force may bedesirable in order to provide suitable adhesion between the solid-stateelectrode and the porous negative electrode.

In an aspect, the buffer composition has a bandgap of greater than 3electron-volts (eV), or greater than 4 eV, and may be thermodynamicallystable against the porous negative electrode, e.g., may be directlyconnected by a tie-line to lithium in the phase diagram and does notsubstantially support the transport of lithium ions.

The buffer composition comprises a binary compound, a ternary compound,a quaternary compound, or a combination thereof. In an aspect, thebuffer layer comprises a buffer composition according to Formula (1)

M_(m)N_(n)Z_(z)H_(h)X_(x)   (1)

wherein

M is Na, K, Rb, Cs, Al, or a metal of Group 2 or 3, or a combinationthereof, wherein

m is 1, 2, 3, or 4,

X is at least one halogen, and wherein x is 0, 1, 2, or 6,

Z is O, S, or a combination thereof, and z is 0, 1, 2, 3, or 4,

n is 0, 1, or 2, and

h is 0, 1, 2, or 3,

provided that x+z+n+h is at least 1.

As used herein, “Group” means a group of the Periodic Table of theElements according to the International Union of Pure and AppliedChemistry (“IUPAC”) Group 1-18 group classification system.

The Group 3 metal may comprise any suitable lanthanide or actinide,e.g., an element having an atomic number from 58 to 71, or 90 to 103.

M in Formula (1) can be K, Rb, Cs, Be, Ca, Sr, Ba, Sc, Y, Th, Al, Lu,Tm, Er, Ho, Dy, Tb, Sm, Nd, Pr, La, Yb, La, or Yb. Use of a lanthanide,such as Eu, Ho, Dy, or Lu is mentioned.

Specific examples of the buffer composition include BeO, SrF₂, KCl,CsCl, RbCl, SrBr₂, ThO₂, CsBr, RbBr, Y₂O₃, AlN, Lu₂O₃, Tm₂O₃, Ba₄I₆O,Er₂O₃, Ho₂O₃, Dy₂O₃, Tb₂O₃, CsI, KI, Sm₂O₃, Sm₂O₂S, RbI, Nd₂O₃, Pr₂O₃,CaO, La₂O₃, YbO, BaI₂, Be₃N₂, La₂SO₂, YbF₂, CaH₂, SrBe₃O₄, or Pr₂SO₂.Mentioned is use of Er₂O₃, Ho₂O₃, or Dy₂O₃. A combination comprising atleast one of the foregoing may be used.

The buffer layer may have any suitable thickness. In an aspect, thebuffer layer has a thickness of 5 to 50 nm, 20 to 40 nm, or 25 to 35 nm.

The porous negative electrode comprises a metal, a transition metalnitride, or a combination thereof. Examples of the metal and transitionmetal include gold, copper, nickel, aluminum, silver, titanium nitride,gallium nitride, molybdenum nitride, or a combination thereof

The metal and transition metal can have a nanostructure. The term“nanostructure” as used herein means a material having a nanofiberstructure, a nanorod structure, a nanowire structure, or a nanotubestructure, or a nanobody, wherein at least one of the dimensions, i.e.,a length, a diameter, or a width of the material may be nano-sized, thatis, has a nanometer scale dimension. Optionally the porous negativeelectrode comprises ordered nanostructures of the metal, the transitionmetal nitride, or a combination thereof. In an aspect, the metal, thetransition metal nitride, or a combination thereof has a nanostructurein the form of nanotubes.

The porous negative electrode may have a porosity of 50 to 95%, 55 to80%, 60 to 75%, optionally 62 to 72%, or 65 to 70%, based on a totalvolume of the negative electrode. The porosity may be determined byscanning electron microscopy. Additional details may be determined byone of skill in the art without undue experimentation.

The porous negative electrode can have an average pore diameter of 25nanometers (nm) to 400 nm, 50 nm to 300 nm, or 100 to 200 nm. The porousnegative electrode may also have a wall thickness of 5 nm to 100 nm, 5nm to 80 nm, 5 to 50 nm, or 5 to 20 nm. The average pore diameter andwall thickness may be determined by scanning electron microscopy, thedetails of which may be determined by one of skill in the art withoutundue experimentation.

Preferably the buffer layer may be disposed in a configuration topreserve the porosity of the porous negative electrode so that lithiummay be deposited within the pores of the porous negative electrode. Inan aspect, the buffer layer is a discontinuous layer and is on a portionof the surface of the porous negative electrode and configured to avoidblocking the pores of the porous negative electrode facing thesolid-state electrolyte. Accordingly the buffer layer is on a portion ofa surface of the porous negative electrode. In an aspect, the bufferlayer is on 0.1 to 50%, 0.3 to 30%, or 0.5 to 10% of a surface of theporous negative electrode, based on a total surface area of the porousnegative electrode. Alternatively or in addition, a portion of thesolid-state electrolyte is directly exposed to a pore of the porousnegative electrode.

In addition to the porous negative electrode and the buffer layer, thebuffered negative electrode-electrolyte assembly also includes asolid-state electrolyte. Any suitable solid state electrolyte may beused. The solid state electrolyte may be, for example, an organic solidelectrolyte, an inorganic solid electrolyte, or a combination thereof.Examples of the organic solid electrolyte may include polyethylene oxideor a derivative thereof, a polypropylene oxide or a derivative thereof,a phosphoric acid ester polymer, poly(L-lysine), polyester sulfide, apolyvinyl alcohol, a polyvinylidene fluoride, and polymers containingionic dissociation groups. The inorganic solid electrolyte may be anoxide-containing solid electrolyte or a sulfide-containing solidelectrolyte. Examples of the oxide-containing solid electrolyte includeat least one of Li_(1+x+y)Al_(x)Ti_(2-x)Si_(y)P_(3-y)O₁₂ (where 0<x<2and 0≤y<3), BaTiO₃, Pb(Zr_(a)Ti_(1-a))O₃ (PZT) (where 0≤a≤1),Pb_(1-x)La_(x)Zr_(1-y) Ti_(y)O₃ (PLZT) (where 0≤x<1 and 0≤y<1),Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN-PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O,MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, Li₃PO₄,Li_(x)Ti_(y)(PO₄)₃ (where 0<x<2 and 0<y<3), Li_(x)Al_(y)Ti_(z)(PO₄)₃(where 0<x<2, 0<y<1, and 0<z<3),Li_(1+x+y)(Al_(a)Ga_(1-a))_(x)(Ti_(b)Ge_(1-b))_(2-x)Si_(y)P_(3-y)O₁₂(where 0≤x≤1, 0≤y≤1, 0≤a≤1, and 0≤b≤1), Li_(x)La_(y)TiO₃ (where 0<x<2and 0<y<3), Li₂O, LiOH, Li₂CO₃, LiAlO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂,or Li_(3+x)La₃M₂O₁₂ (where M is Te, Nb, or Zr, and 0≤x≤10). Theoxide-containing solid electrolyte may be, for example, a garnet-typesolid electrolyte, e.g., Li₇La₃Zr₂O₁₂ (LLZO) orLi_(3-x)La₃Zr_(2-a)M_(a)O₁₂ (M-doped LLZO, where M is Ga, W, Nb, Ta, orAl, and 0≤x≤10 and 0≤a<2). Use of a LISICON compound, e.g.,Li_(2+2x)Zn_(1-x)GeO₄, wherein 0<x<1 is also mentioned.

In an aspect, the solid electrolyte may be, for example, asulfide-containing solid electrolyte. Examples of the sulfide-containingsolid electrolyte may include at least one of Li₂S—P₂S₅, Li₂S—P₂S₅—LiX(where X is a halogen element), Li₂S—P₂S₅—Li₂O, Li₂S—P₂S₅—Li₂O—LiI,Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—LiBr, Li₂S—SiS₂—LiCl,Li₂S—SiS₂—B₂S₃—LiI, Li₂S—SiS₂—P₂S₅—LiI, Li₂S—B₂S₃, Li₂S—P₂S₅—Z_(m)S_(n)(where m and n each are a positive number, Z represents any of Ge, Zn,and Ga), Li₂S—GeS₂, Li₂S—SiS₂—Li₃PO₄, Li₂S—SiS₂—Li_(p)MO_(q) (where pand q each are a positive number, M represents at least one of P, Si,Ge, B, Al, Ga, or In), Li_(7-x),PS_(6-x)Cl_(x) (where 0≤x≤2),Li_(7-x)PS_(6-x)Br_(x) (where 0≤x≤2), or Li_(7-x)PS_(6-x)I_(x) (where0≤x≤2). The sulfide-containing solid electrolyte may be prepared bymelting and quenching starting materials (e.g., Li₂S or P₂S₅), ormechanical milling the starting materials. Subsequently, the resultantmay be heat-treated. The sulfide-containing solid electrolyte may beamorphous or crystalline and may be a mixed form thereof.

Also, the sulfide-containing solid electrolyte may include at leastsulfur (S), phosphorus (P), and lithium (Li), as component elementsamong the sulfide-containing solid electrolyte materials. For example,the sulfide-containing solid electrolyte may be a material includingLi₂S—P₂S₅. Here, when the material including Li₂S-P₂S₅ is used as asulfide-containing solid electrolyte material, a mixing molar ratio ofLi₂S and P₂S₅ (Li₂S:P₂S₅) may be, for example, selected in a range ofabout 50:50 to about 90:10.

For example, the sulfide-containing solid electrolyte may include anargyrodite-type solid electrolyte represented by Formula (2):

Li⁺ _(12-n-x)A^(n+)X²⁻ _(6-x)Y⁻ _(x)   (2)

In Formula (2), A is at least one of P, As, Ge, Ga, Sb, Si, Sn, Al, In,Ti, V, Nb, or Ta, X is at least one of S, Se, or Te, Y is at least oneof Cl, Br, I, F, CN, OCN, SCN, or N₃, 1≤n≤5, and 0≤x≤2.

The sulfide-containing solid electrolyte may be an argyrodite-typecompound including at least one of Li_(7-x)PS_(6-x)Cl_(x) (where 0≤x≤2),Li_(7-x)PS_(6-x)Br_(x) (where 0≤x≤2), or Li_(7-x)PS_(6-x)I_(x) (where0≤x≤2). Particularly, the sulfide-containing solid electrolyte in thesolid electrolyte layer 30 may be an argyrodite-type compound includingat least one of Li₆PS₅Cl, Li₆PS₅Br, or Li₆PS₅I.

The buffered negative electrode-electrolyte assembly can be manufacturedby sputtering the buffer composition on the porous negative electrode toform a coated porous negative electrode; and disposing a solid-stateelectrolyte on the coated porous negative electrode to manufacture thebuffered negative electrode-electrolyte assembly.

Also disclosed is an electrochemical cell (10), such as a lithiumbattery, comprising a positive electrode (12); and the buffered negativeelectrode-electrolyte assembly (15) as described herein on the positiveelectrode (12).

A schematic diagram of a lithium battery is provided in FIG. 9. As shownin the battery 100 of FIG. 9, a positive electrode 110 can be used incombination with a buffered negative electrode-electrolyte assemblywhich includes a porous negative electrode 101, a solid-stateelectrolyte 120, wherein the buffer layer is between the porous negativeelectrode 101 and solid-state electrolyte 120. The positive electrodeand the buffered negative electrode-electrolyte assembly can be wound orfolded and accommodated in a battery case or pouch 130. The battery canalso include a cap 140.

The positive electrode may comprise a positive active material layerincluding a positive active material on a current collector. The currentcollector may comprise aluminum, for example. The positive electrode maybe prepared by screen printing, slurry casting, or powder compression ofthe positive active material on the current collector to provide thepositive electrode. However, the method of preparing the positiveelectrode is not limited thereto, and any suitable method may be used.

The positive active material can comprise a lithium transition metaloxide, or a transition metal sulfide. For example, the positive activematerial can be a compound represented by any of the Formulas:Li_(a)A_(1-b)M_(b)D₂ wherein 0.90≤a≤1.8 and 0≤b≤0.5;Li_(a)E_(1-b)M_(b)O_(2-c)D_(c) wherein 0.90≤a≤1.8, 0≤b≤0.5, and0≤c≤0.05; LiE_(2-b)M_(b)O_(4-c)D_(c) wherein 0≤b≤0.5 and 0≤c≤0.05;Li_(a)Ni_(1-b-c)Co_(b)M_(c)D_(αa) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,and 0<α≤2; Li_(a)Ni_(1-b-c)Co_(b)M_(c)O_(2-α)X_(α) wherein 0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, and 0<α<2; Li_(a)Ni_(1-b-c)CO_(b)M_(c)O_(2-α)X₂wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<a<2;Li_(a)Ni_(1-b-c)Mn_(b)M_(c)D_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05,and 0<a≤2; Li_(a)Ni_(1-b-c)Mn_(b)M_(c)O_(2-a)X_(α) wherein 0.90≤a≤1.8,0≤b≤0.5, 0≤c≤0.05, and 0<α<2; Li_(a)Ni_(1-b- c)Mn_(b)M_(c)O_(2-α)X₂wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2;Li_(a)Ni_(b)E_(c)G_(d)O₂ wherein 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and0.001≤d≤0.1; Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ wherein 0.90≤a≤1.8, 0≤b≤0.9,0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1; Li_(a)NiG_(b)O₂ wherein 0.90≤a≤1.8and 0.001≤b≤0.1; Li_(a)CoG_(b)O₂ wherein 0.90≤a≤1.8 and 0.001≤b≤0.1;Li_(a)MnG_(b)O₂ where 0.90≤a≤1.8 and 0.001≤b≤0.1; Li_(a)Mn₂G_(b)O₄wherein 0.90≤a≤1.8 and 0.001≤b≤0.1; QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₂;LiRO₂; LiNiVO₄; Li_((3-f))J₂(PO₄)₃ (0≤f≤2); Li_((3-f))Fe₂(PO₄)₃ wherein0≤f≤2; and LiFePO₄, in which in the foregoing positive active materialsA is Ni, Co, or Mn; M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, or arare-earth element; D is O, F, S, or P; E is Co or Mn; X is F, S, or P;G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V; Q is Ti, Mo or Mn; R is Cr,V, Fe, Sc, or Y; and J is V, Cr, Mn, Co, Ni, or Cu. Examples of thepositive active material include LiCoO₂, LiMn_(x)O_(2x) where x=1 or 2,LiNi_(1-x)Mn_(x)O_(2x) where 0<x<1, LiNi_(1-x-y) Co_(x)Mn_(y)O₂ where0≤x≤0.5 and 0≤y≤0.5, LiFePO₄, TiS₂, FeS₂, TiS₃, and FeS₃. For example,the positive active material can include a composite oxide of lithiumand a metal selected from cobalt, manganese, and nickel. Mentioned areNMC 811 (LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂), NMC 622(LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂), NMC 532 (LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂),and NCA (LiNi_(0.8)Co_(0.15)Al_(0.05)O₂).

The positive active material layer may further include a conductiveagent and a binder. Any suitable conductive agent and binder may beused.

A binder can facilitate adherence between components of the electrode,such as the positive active material and the conductor, and adherence ofthe electrode to a current collector. Examples of the binder can includepolyacrylic acid (PAA), polyvinylidene fluoride, polyvinyl alcohol,carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM),sulfonated EPDM, styrene-butadiene-rubber, fluorinated rubber, acopolymer thereof, or a combination thereof. The amount of the bindercan be in a range of about 1 part by weight to about 10 parts by weight,for example, in a range of about 2 parts by weight to about 7 parts byweight, based on a total weight of the positive active material. Whenthe amount of the binder is in the range above, e.g., about 1 part byweight to about 10 parts by weight, the adherence of the electrode tothe current collector may be suitably strong.

The conductive agent can include, for example, carbon black, carbonfiber, graphite, carbon nanotubes, graphene, or a combination thereof.The carbon black can be, for example, acetylene black, Ketjen black,Super P carbon, channel black, furnace black, lamp black, thermal black,or a combination thereof. The graphite can be a natural graphite or anartificial graphite. A combination comprising at least one of theforegoing conductive agents can be used. The positive electrode canadditionally include an additional conductor other than the carbonaceousconductor described above. The additional conductor can be anelectrically conductive fiber, such as a metal fiber; a metal powdersuch as a fluorinated carbon powder, an aluminum powder, or a nickelpowder; a conductive whisker such as a zinc oxide or a potassiumtitanate; or a polyphenylene derivative. A combination comprising atleast one of the foregoing additional conductors can be used.

Specific examples of buffered negative electrode-electrolyte assemblyare illustrated in FIGS. 5 and 6. In an aspect, the buffer layer (16)may be disposed on the root (50) of the nanostructure in the porousnegative electrode (18) as shown in FIG. 5. In another aspect, thebuffer layer may be a conformal coating (55) and be disposed on the rootof the nanostructure of the porous negative electrode (18) as shown inFIG. 6. While not wanting to be bound by theory, it is understood thatas the cell is cycled, lithium may deposit in the pore (60) of theporous negative electrode (18), e.g., within the pore (18) and on asurface of the solid electrolyte (18) facing the negative electrode.Because the lithium is deposited in the pore of the porous negativeelectrode, the volume of the lithium can be accommodated, avoidingdetachment of the solid-state electrolyte from the porous negativeelectrode as the volume of the deposited lithium increases. Also, byavoiding deposition of lithium at the root of the porous negativeelectrode, the bond between the solid state electrolyte and the root ofthe nanostructured negative electrode provided by the buffer layer ispreserved. While not wanting to be bound by theory, it is understoodthat these features contribute to the observed improved cellperformance.

An electrochemical cell can be manufactured by disposing a buffer layeras described herein between a solid-state electrolyte and a porousnegative electrode to form buffered negative electrode-electrolyteassembly and disposing a positive electrode on the solid-stateelectrolyte to manufacture the electrochemical cell.

Hereinafter an embodiment is described in further detail. The examplesare provided for illustrative purposes only and are not intended tolimit the scope of the present disclosure.

EXAMPLES Example 1: Preparation of Erbium (III) Oxide Coated TitaniumNitride Electrode

Sputtering of Er₂O₃ is achieved with an RF power supply (e.g. DresslerRFX600A) under inert gas at around 40 mtorr pressure, after evacuatingthe chamber at least to a vacuum of 10⁻⁶ torr. TiN substrates werepreloaded into the chamber with a Er₂O₃ target installed. TiN were thencoated with Er₂O₃ with a rate of around 0.5 Å/s.

The erbium (III) oxide coated titanium nitride electrode was analyzedusing scanning electron microscopy (SEM) (e.g. JEOL 5910). The resultsare shown in FIGS. 7A and 7B. The figures show that Er₂O₃ (46) is coatedon the root of the titanium nitride nanostructures (45). Er₂O₃ coatingcan be identify by a brighter hue due to its electronic insulatingproperties.

Example 2: Preparation of Lithium Batteries

A coin cell battery was assembled in an argon atmosphere with erbium(III) oxide coated titanium nitride electrode, PEO (polyethylene oxide)film as electrolyte, and lithium metal disk as source for lithium ions.The cell was cycled at 60° C. at a current density of 0.5 mA/cm².

The results are shown in FIGS. 8A and FIG. 8B. The electrochemicalcharacterization shows that cell with the buffer layer can cycle for >50hours at 0.05 mA/cm².

Comparative Example 1

A cell will be assembled using the same method as in Example 1, butwithout buffer layer. The cell without the buffer layer will not be ableto be cycled.

Various embodiments are shown in the accompanying drawings. Thisinvention may, however, be embodied in many different forms, and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the scope of the invention to thoseskilled in the art. Like reference numerals refer to like elementsthroughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be present therebetween. In contrast, when an element isreferred to as being “directly on” another element, there are nointervening elements present.

It will be understood that, although the terms “first,” “second,”“third,” etc. may be used herein to describe various elements,components, regions, layers, or sections, these elements, components,regions, layers, or sections should not be limited by these terms. Theseterms are only used to distinguish one element, component, region,layer, or section from another element, component, region, layer orsection. Thus, “a first element,” “component,” “region,” “layer,” or“section” discussed below could be termed a second element, component,region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “At least one” is not to be construed as limiting “a” or“an.” “Or” means “and/or.” It will be further understood that the terms“comprises” and/or “comprising,” or “includes” or “including” when usedin this specification, specify the presence of stated features, regions,integers, steps, operations, elements, or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, or groupsthereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to crosssection illustrations that are schematic illustrations of idealizedembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, embodiments described herein should not beconstrued as limited to the particular shapes of regions as illustratedherein but are to include deviations in shapes that result, for example,from manufacturing. For example, a region illustrated or described asflat may, typically, have rough and/or nonlinear features. Moreover,sharp angles that are illustrated may be rounded. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the precise shape of a region and are notintended to limit the scope of the present claims.

While a particular embodiment has been described, alternatives,modifications, variations, improvements, and substantial equivalentsthat are or may be presently unforeseen may arise to applicants orothers skilled in the art. Accordingly, the appended claims as filed andas they may be amended are intended to embrace all such alternatives,modifications variations, improvements, and substantial equivalents.

What is claimed is:
 1. A buffered negative electrode-electrolyteassembly comprising: a porous negative electrode comprising a metal, atransition metal nitride, or a combination thereof; a solid-stateelectrolyte; and a buffer layer between the porous negative electrodeand the solid-state electrolyte, the buffer layer comprising a buffercomposition according to Formula (1)M_(m)N_(n)Z_(z)H_(h)X_(x)   (1) wherein M is Na, K, Rb, Cs, Al, or ametal of Group 2 or 3, or a combination thereof, wherein m is 1, 2, 3,or 4, X is at least one halogen and wherein x is 0, 1, 2, or 6, Z is O,S, or a combination thereof, and z is 0, 1, 2, 3, or 4, n is 0, 1, or 2,and h is 0, 1, 2, or 3, provided that x+z+n+h is at least 1, and whereinthe buffer composition has an electronic conductivity that is less thanor equal to 1×10⁻² times an electronic conductivity of the solid-stateelectrolyte, and the buffer composition has an ionic conductivity lessthan or equal to 1×10⁻⁶ times an ionic conductivity of the solid-stateelectrolyte.
 2. The assembly of claim 1, wherein the buffer compositionhas a bandgap greater than 3 electron-volts.
 3. The assembly of claim 1,wherein the buffer composition comprises a binary compound.
 4. Theassembly of claim 1, wherein M in Formula (1) is K, Rb, Cs, Be, Ca, Sr,Ba, Sc, Y, Th, Al, Lu, Tm, Er, Ho, Dy, Tb, Sm, Nd, Pr, La, Yb, La, orYb.
 5. The assembly of claim 1, wherein the buffer composition comprisesat least one of BeO, SrF₂, KCl, CsCl, RbCl, SrBr₂, ThO₂, CsBr, RbBr,Y₂O₃, AlN, Lu₂O₃, Tm₂O₃, Ba₄I₆O, Er₂O₃, Ho₂O₃, Dy₂O₃, Tb₂O₃, CSI, KI,Sm₂O₃, Sm₂O₂S, RbI, Nd₂O₃, Pr₂O₃, CaO, La₂O₃, YbO, BaI₂, Be₃N₂, La₂SO₂,YbF₂, CaH₂, SrBe₃O₄, or Pr₂SO₂.
 6. The assembly of claim 1, wherein thebuffer layer has a thickness of 5 to 50 nm.
 7. The assembly of claim 1,wherein the buffer layer is a conformal coating on a surface of theporous negative electrode.
 8. The assembly of claim 1, wherein thebuffer layer is on a portion of a surface of the porous negativeelectrode.
 9. The assembly of claim 1, wherein a portion of thesolid-state electrolyte is directly exposed to a pore of the porousnegative electrode.
 10. The assembly of claim 1, wherein the porousnegative electrode has an average pore diameter between 25 nm and 400 nmand a wall thickness of 5 nm to 100 nm.
 11. The assembly of claim 1,wherein the porous negative electrode has a porosity of 60% to 75%. 12.The assembly of claim 1, wherein the porous negative electrode comprisesthe transition metal nitride.
 13. The assembly of claim 1, wherein thesolid-state electrolyte comprises an organic solid electrolyte, anoxide-containing inorganic solid electrolyte, a sulfide-containinginorganic solid electrolyte, or a combination thereof.
 14. Anelectrochemical cell comprising: a positive electrode; and the bufferednegative electrode-electrolyte assembly of claim 1 on the positiveelectrode.
 15. The electrochemical cell of claim 14, wherein thepositive electrode comprises a lithium transition metal oxide, a lithiumtransition metal phosphate, or a combination thereof.
 16. A method ofmanufacturing a electrochemical cell, the method comprising: disposing abuffer layer between a solid-state electrolyte and a porous negativeelectrode, the porous negative electrode comprising a metal, atransition metal nitride, or a combination thereof, to form a bufferednegative electrode-electrolyte assembly; and disposing a positiveelectrode on the solid-state electrolyte to manufacture theelectrochemical cell, wherein the buffer layer comprises a buffercomposition according to Formula (1)M_(m)N_(n)Z_(z)H_(h)X_(x)   (1) wherein M is Na, K, Rb, Cs, Al, a metalof Group 2 or 3, or a combination thereof, wherein m is 1, 2, 3, or 4, Xis at least one halogen and wherein x is 0, 1, 2, or 6, Z is O, S, or acombination thereof, and z is 0, 1, 2, 3, or 4, n is 0, 1, or 2, and his 0, 1, 2, or 3, provided that x+z+n+h is at least 1, and wherein thebuffer composition has an electronic conductivity that is 1×10⁻⁸ to1×10⁻² times an electronic conductivity of the solid-state electrolyte,and the buffer composition has an ionic conductivity less than or equalto 1×10⁻⁶ times an ionic conductivity of the solid-state electrolyte.